While filming a documentary about monsters, filmmaker Adam Green is contacted by an ex-police officer who believes he has found the entrance to their underground world.

Digging Up The Marrow has no trailer, no teasers, and barely a poster to signal its existence. And that is exactly how writer-director Adam Green wants to present it to you.

Inspired by the true story of a fan that contacted Green and informed him that Victor Crowley is real and he’d got his story all wrong, the film took four years to complete and is, by all accounts, a labour of love. It’s also one of the most remarkable, modern horror movies you’re likely to see.

Filmed in the style of a documentary – it’s more of a mockumentary even though, as Green argues, it isn’t exactly Spinal Tap – Marrow follows the man himself, along with his buddy Will Barratt, as they embark upon a strange journey to discover whether monsters are, in fact, real. The always welcome Ray Wise plays grizzled former cop William Dekker, a man who claims to know where the entrance to the monsters’ secret world (the Marrow of the title) lays, and who agrees to take Green, Barratt and their many cameras there. To say any more would risk spoiling the fun, and this is the definition of a film one must go into completely green (no pun intended), but suffice to say nothing is what it seems and anything is possible.

Anyone who’s grown up feeling more at home on the dark side will find plenty to love about Digging Up The Marrow, which opens with testimonies from horror experts such as Lloyd Kaufman, Evan Dickson and even Green’s dearly-departed buddy Dave Brockie who proclaims, in full Oderus Orgungus getup, that he’s always been a monster and when he dies, he’ll be a dead monster. Green’s buddies pop up all over the place throughout the flick, but Kane Hodder (who starred as Victor Crowley in Green’s Hatchet trilogy) steals the show as he watches creepy footage with the eager filmmaker only to dismiss it all as a hoax – “Found footage, that hasn’t been done before” he quips, dashing his hopes.

The many additions of “real” people give Marrow a more realistic, documentary feel in spite of the casting of Wise. Green was conscious that audiences might think they were being tricked, hence his decision to cast a known actor in the lead role, but certain commentators have called bullshit on this, claiming they believed the film to be the real deal until he showed up as Dekker. This argument is, of course, ridiculous as anyone who has caught the film can attest – it’s about monsters, after all.

Digging Up The Marrow is an old school horror flick. There is no violence or gore whatsoever, and yet the tension and the threat are so real, it’s suffocating even when it goes a bit ghost train-y, with a succession of incredibly effective jump scares – none of which are cued by the usual screech of violins, thankfully. Green is a proponent of practical effects over CGI, with his Hatchet series in particular making a case for the resurgence of gooey latex. He notes that horror “is scariest when it’s real” and, without giving too much away, the SFX in Marrow prove even further that there is something much more frightening about an actual, three-dimensional presence, which simply cannot be replicated on a computer. The film’s title is inspired by an art show that Green’s friend Alex Pardee did about monsters, and the attention to detail really shows, even down to the gorgeous poster artwork.

Considering it’s presented as a documentary, and might be seen by some as a really weird vanity project, Green chooses to present himself in a nicely self-deprecating manner. We’re first introduced to him as Barratt suggests that maybe they should hire an actor to play him, and his eye-rolling, yet ultimately desperate-to-believe, childlike reactions to Dekker’s claims make his outlandish stories come to life. The film also provides an interesting look into the inner workings behind Green’s production company Ariescope, and even his home life (though he was quick to point out that he did not use his real house for filming) with his wife, whom he has since divorced. It’s rare that we get such an insight into the personal life of a filmmaker, even one as open as Green, so it’s nice to be allowed in a little bit.

In spite of its well-judged undercurrent of self-referential humour – and it is very funny – Digging Up The Marrow is a profoundly scary film. Green himself starts off as a bit of sceptic, and his reactions to Dekker’s increasingly wild claims make the first act slip by without the audience realising they are being lulled into a false sense of security, allowing for one of the greatest frights in modern horror to occur – and it really must be experienced, words cannot do it justice. The closing sequence is truly terrifying, especially considering what’s come before it, and it’s impossible to look away even though hiding behind one’s hands seems like the smartest option. It’s testament to Green’s skills as a filmmaker, and indeed his knowledge as a horror fan, that Marrow moves along so seamlessly in spite of its lack of any obvious narrative structure. When the end comes, it’s a shock – as well it should be.

Digging Up The Marrow is not the best horror movie you’re going to see this year, because chances are you won’t get to see it. But it is the best horror release of the year by far, even without a release, and it further proves that Adam Green is one of the most interesting filmmakers currently working within the genre. If you’ve never taken him seriously before, now is the time to start.